1. Field of the Invention
The present invention relates to the electro-mechanical arts and energy storage systems. In particular, the present invention pertains to mechanical energy exchange systems coupled with electrical energy exchange systems.
2. Description of Related Art
Electro-mechanical energy exchange systems have provided mechanical and electrical power solutions for over one hundred years. These solutions have typically involved a prime mover driving an AC generator at a fixed speed multiple of the synchronous frequency. These power solutions have not required electronic processing of the generator output since the generator is a constant speed machine able to generate a sinusoidal electric output at the desired fixed frequency.
Advanced mechanical energy storage devices like high speed flywheels pose new challenges to traditional electro-mechanical energy exchange solutions. No longer able to rely on fixed speed operation and the attendant fixed frequency of a connected AC generator, these new systems require that each watt of electric power produced in a variable speed generator be processed through power electronics using semiconductor switches to synthesize a fixed frequency AC output.
With the need to process variable frequency AC power using power electronics comes the need for high speed semiconductor switching devices. At high shaft speeds and hence high electrical frequencies, the resolution of command voltages used to switch the semiconductors on and off decreases due to a fixed semiconductor switching frequency. This creates difficulties with feedback control techniques typically used to control these systems since the assumptions of continuous-time control theory typically used to develop feedback controllers become less appropriate.